In the communication system in which the external device and the electronic device are connected to each other via the signal cable, the electronic device receives a voltage from the external device to output a signal indicating connection with the external device. As a device of this type, for example, there is known a HDMI (High-Definition Multimedia Interface) device that includes an interface HDMI Standard.
The HDMI is a standard concerning a communication interface for transmitting a video/audio through a digital signal. In recent years, there have been provided various devices including interfaces compliant with the HDMI Standard.
The communication system based on the HDMI Standard includes a source device for outputting a HDMI signal, and a sink device for receiving the HDMI signal. The source device and the sink device are connected to each other via a HDMI cable (refer to Patent Literature 1).
The source device is, for example, a Blu-ray display player, a video camera, or a portable device. The sink device is, for example, a monitor or a projector such as a HD (High Definition) television.
In the aforementioned communication system, when the source device and the sink device are connected to each other via the HDMI cable, processing for transmitting the HDMI signal between the source device and the sink device is executed.
FIG. 1 illustrates an example of a HDMI signal transmission/reception sequence.
Referring to FIG. 1, first, the source device supplies a predetermined voltage (e.g., +5 V) to the sink device (step S100). The sink device that has received the voltage transmits a hot-plug detection signal to the source device (step S101).
The source device recognizes that it is connected to the sink device on the basis of the hot-plug detection signal from the sink device.
The source device that has received the hot-plug detection signal executes access to EDID (Extended Display Identification Data) information in the sink device (step S102). The sink device transmits the EDID information that it holds to the source device (step S103). The EDID information is a data set indicating information regarding the corresponding function or performance (specifically, format or resolution) of the sink device.
The source device recognizes the format or the resolution of a video/audio reproducible by the sink device on the basis of the EDID information acquired from the sink device, and transmits a video/audio signal, corresponding to the format or to the resolution, to the sink device by a TMDS (Transition Minimized Differential Signaling) method (step S104).
The sink device receives the TMDS signal from the source device (step S105). In addition to the TMDS signal, a clock signal and a control signal are supplied from the source device to the sink device. The sink device executes processing such as reproduction of the TMDS signal on the basis of the clock signal according to the control signal.
FIG. 2 illustrates a configuration example of the sink device.
Referring to FIG. 2, the sink device includes HDMI connector 101, memory 102, and HDMI receiver IC (integrated circuit) 103.
Memory 102 is a nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory), and stores the EDID information.
HDMI connector 101 is a standard-type connector having 19 pins. The 19-th pin is a pin for outputting the hot-plug detection signal. The voltage of +5 V from the source device is supplied to the 18-th pin.
The 18-th pin is connected to the 19-th pin via a resistive element. When the voltage of +5 V is supplied to the 18-th pin, current flows through the resistive element, and the hot-plug detection signal (+5 V) is output from the 19-th pin.
The 15-th and 16-th pins are pins for reading the EDID information stored in memory 102. The 15-th and 16-th pins are connected to memory 102 and HDMI receiver IC 103.
The TMDS signal, the clock signal, and the control signal from the source device are received by some of the remaining pins. HDMI receiver IC 103 executes reproduction processing of the TMDS signal on the basis of the clock signal according to the control signal.
FIG. 3 illustrates another configuration example of the sink device.
The sink device illustrated in FIG. 3 is configured such that memory 102 is removed from the sink device illustrated in FIG. 2 and HDMI receiver IC 103 stores EDID information 104.
In the sink device illustrated in FIG. 3, HDMI receiver IC 103 is accessed from the source device via the 15-th and 16-th pins, and outputs EDID information 104 that it holds from the 15-th and 16-th pins. Other operations are similar to those illustrated in FIG. 2.
Both the sink devices illustrated in FIGS. 2 and 3 output, irrespective of whether the sink device is in a power-ON state, hot-plug detection signals of +5 V from the 19-th pin when the voltage of +5 V is supplied to the 18-th pin.